Conventionally, for instance, as disclosed in Japanese Unexamined Patent Publication No. 196208/1982, a resin compound containing an epoxy resin or polyphenylene sulfide in which 30 to 80% by weight of spherical quartz glass fine particles are filled is used for parts for optical communication such as a ferrule for an optical connector, which are precision parts. Ingredients of the above resin (epoxy resin) compound and the properties of a ferrule for an optical connector produced therefrom are shown in Table 1.
TABLE 1 __________________________________________________________________________ Ingredients of resin compound Quartz glass fine particles content Properties of ferrules (having an average particle Precision Connectability Conventional diameter of about 10 .mu.m) Circularity Surface roughness Optical loss Examples (% by weight) (.mu.m) (.mu.m) (dB) __________________________________________________________________________ 1 29.5 1.2 0.6 0.70 2 49.7 1.1 0.6 0.68 3 69.5 1.2 -- 0.60 4 81.0 -- 0.7 0.68 __________________________________________________________________________
From the properties of the ferrules shown in Table 1, it can be seen that the ferrule for an optical connector molded by using the resin compound containing the above spherical fine particles is excellent in optical loss during connecting with an optical fiber being at most 1 dB since circularity is about 1 .mu.m and surface roughness is at most 1 .mu.m.
Also, spherical fine particles are filled in a conventional resin compound as a filler. Therefore, it is known that distribution of the filler contained in a molded article and mold shrinkage become uniform and that dimensional precision of a molded article is increased. Also, the filler contained therein is composed of fine particles having an average particle diameter of about 10 .mu.m. Therefore, it is also known that surface roughness of a molded article is small and a molded article is excellent in surface smoothness.
As mentioned above, the dimensional precision of a resulting molded article is increased by a conventional resin compound. However, there arises a problem that the contact area between the filler and the resin becomes small, so that mechanical strength of a molded article becomes low since the shape of the filler is spherical. Also, when the amount of the filler is increased in order to lower its coefficient of thermal expansion, there arise problems that moldability is lowered and that dimensional precision is lowered since contact friction of the fillers with each other is increased and melt viscosity of the resin compound is increased.
Also, the precision parts for an optical connector, made of a conventional resin compound, have advantages that circularity is high and that optical loss is small during connecting with an optical fiber. However, the mechanical strength is low. Therefore, there arises a problem that reliability is low during connecting with an optical fiber. Also, when coefficient of thermal expansion of precision parts for an optical connector is lowered by increasing the amount of the filler contained in a resin compound in order to lower the optical loss in accordance with the change of temperature during connecting with an optical fiber, melt viscosity of the resin compound becomes high. Therefore, there arise problems that moldability is lowered and that it becomes difficult to give precision parts for an optical connector, which are high in dimensional precision and small in optical loss during connecting with an optical fiber.
The present invention has been accomplished in consideration of the above-mentioned prior art.
An object of the present invention is to provide a resin compound which increases mechanical strength without impairment of dimensional precision, surface smoothness and low thermal expansive property, and which is suitable for, e.g. molding precision parts.
Another object of the present invention is to provide a resin compound which can lower the coefficient of thermal expansion without impairment of moldability.
The other object of the present invention is to provide a sleeve and a ferrule which are high in reliability during connecting with an optical fiber.